orbital mechanics :D

.gitignore

@@ -1 +1,5 @@
 /target
+
+# ffmpeg -framerate 60 -i recordings/%05d.png -pix_fmt yuv420p recording.mp4
+/recordings
+/recording.mp4

Cargo.lock

@@ -2240,6 +2240,7 @@ name = "sketch-gravity"
 version = "0.1.0"
 dependencies = [
  "nannou",
+ "once_cell",
  "rayon",
 ]
 

Cargo.toml

@@ -7,4 +7,5 @@ edition = "2018"
 
 [dependencies]
 nannou = "0.17.1"
+once_cell = "1.8.0"
 rayon = "1.5.1"

src/main.rs

@@ -1,14 +1,21 @@
 use nannou::prelude::*;
 use rayon::prelude::*;
 
+mod recording;
+
 fn main() {
-    nannou::app(model).update(update).simple_window(view).run();
+    nannou::app(model)
+        .size(1440, 1440)
+        .update(update)
+        .simple_window(view)
+        .run();
 }
 
 #[derive(Clone)]
 struct Body {
     pos: DVec2,
     vel: DVec2,
+    mass: i64,
 }
 
 struct Model {
@@ -18,17 +25,33 @@ struct Model {
 fn model(_app: &App) -> Model {
     let mut bodies = Vec::new();
 
-    let mut theta = 0.0;
-    for r in 0..512 {
-        let r = r as f64;
-        let r = 10.0 * r.sqrt();
+    const MASS_SUN: i64 = 150000000000000000;
+
+    bodies.push(Body {
+        pos: (0.0, 0.0).into(),
+        vel: (0.0, 0.0).into(),
+        mass: MASS_SUN,
+    });
+
+    const G: f64 = 6.67408e-11;
+
+    const COPIES: i32 = 1;
+
+    let d_theta: f64 = (360.0 / COPIES as f64).to_radians();
+
+    for i in 0..COPIES {
+        let theta = i as f64 * d_theta;
+
+        for i in 10..250 {
+            let r = 5.0 * i as f64;
+            let m = 10000000 / i;
 
             bodies.push(Body {
                 pos: (r * theta.cos(), r * theta.sin()).into(),
-            vel: (0.0, 0.0).into(),
+                vel: (0.0, (G * MASS_SUN as f64 / r).sqrt()).into(),
+                mass: m,
             });
-
-        theta += 1.94161103873;
+        }
     }
 
     Model { bodies }
@@ -38,7 +61,7 @@ fn update(app: &App, model: &mut Model, _update: Update) {
     const G: f64 = 6.67408e-11;
 
     let bodies = model.bodies.clone();
-    let delta_t = app.duration.since_prev_update.as_secs_f64();
+    let delta_t = recording::delta_t(&app);
 
     model
         .bodies
@@ -59,10 +82,9 @@ fn update(app: &App, model: &mut Model, _update: Update) {
                     return;
                 }
 
-                let force = G * /* × mass_a × mass_b = */ 1e14 / dist_sq;
+                let acceleration = G * other_body.mass as f64 / dist_sq;
 
-                acc += delta * force / dist_sq.sqrt();
-                acc -= 0.5 * delta / (dist_sq * 0.5);
+                acc += delta * acceleration / dist_sq.sqrt();
             });
 
             body.vel += acc * delta_t;
@@ -73,12 +95,14 @@ fn update(app: &App, model: &mut Model, _update: Update) {
 fn view(app: &App, model: &Model, frame: Frame) {
     // let t = app.duration.since_start.as_secs_f64();
 
-    let draw = app.draw();
+    let draw = app.draw().scale(2.0);
     draw.background().color(BLACK);
 
     for body in model.bodies.iter() {
-        draw.ellipse().w_h(10.0, 10.0).xy(body.pos.as_f32());
+        let diameter = (body.mass as f32).log10(); // should be proportional to cuberoot but this is so we can actually see the small ones
+        draw.ellipse().w_h(diameter, diameter).xy(body.pos.as_f32());
     }
 
     draw.to_frame(app, &frame).unwrap();
+    recording::record(app, &frame);
 }

src/recording.rs

@@ -0,0 +1,33 @@
+use nannou::prelude::*;
+use once_cell::sync::Lazy;
+
+static RECORDING: Lazy<bool> = Lazy::new(|| {
+    let args: Vec<String> = std::env::args().collect();
+    args.iter().any(|s| s == "--record")
+});
+
+pub fn record(app: &App, frame: &Frame) {
+    if !*RECORDING {
+        return;
+    }
+    // save frame
+    let path = app
+        .project_path()
+        .expect("failed to locate `project_path`")
+        // Capture all frames to a directory called `/<path_to_nannou>/nannou/simple_capture`.
+        .join("recordings")
+        // Name each file after the number of the frame.
+        .join(format!("{:05}", frame.nth()))
+        // The extension will be PNG. We also support tiff, bmp, gif, jpeg, webp and some others.
+        .with_extension("png");
+    println!("frame: {} {:.05}", frame.nth(), frame.nth() as f32 / 60.0);
+    app.main_window().capture_frame(path);
+}
+
+pub fn delta_t(app: &App) -> f64 {
+    if *RECORDING {
+        1.0 / 60.0
+    } else {
+        app.duration.since_prev_update.as_secs_f64()
+    }
+}